There is intense interest in the synthesis of the title molecules since they are commonly found as subunits of biologically potent nature products such as polyether antibiotics, antiparasitic agents, molluscicidal glycoalkaloids, marine and plant toxins, and a number of insect pheromones. Therefore, one major objective in this field is associated with the development of chiral synthetic methodologies, i.e. techniques that are needed for synthesizing the biologically active form of a chiral molecule without also synthesizing its mirror image. In recent years we found a synthetic strategy that allowed the efficient preparation of crystalline spiroketals and vinylic ethers with significant stereoselectivity through thermodynamically phenylsulfonyl group induced and stereocontrolled spirocyclization for dihydroxyketone equivalents. Our long term interest is to design and prepare chemicals that contribute to the development of molecular probes or drugs for parasitic and virus- related studies. Specifically, the present project will test the general applicability of the stereoselective method and its extention to novel nitrogen heterocycles through the synthesis of the following compound classes: 1) Alkylsubstituted spiroketals, 2) Alkylsubstituted Spiroaminoketals, 3) Functionalyzed Vinylic Ethers, 4) Functionalyzed Enamines. As secondary objectives and following the synthetic work the biomedical potential of the obtained compounds will be evaluated by means of: 1) Antibiotic Assays, 2) Antiviral Assays.